栈的弹出压入序列
https://leetcode.cn/problems/min-stack/description/
class Solution {
public:

    bool IsPopOrder(vector<int>& pushV, vector<int>& popV) {
        stack<int> st;
        int pushi=0,popi=0;
        while(pushi<pushV.size())
        {
            st.push(pushV[pushi++]);
            while(!st.empty()&&st.top()== popV[popi])
            {
                st.pop();
                ++popi;
            }
        }
       return st.empty();
    }
};